The present invention is directed to reinforced hollow tubes and their methods of manufacture and use. A specific application of the present invention is for arterial and venous cardiopulmonary bypass (CPB) cannulas. The present invention is particularly useful as the arterial return cannula for the cardiopulmonary bypass system described in co-pending U.S. patent application Ser. No. 08/282,192 which is incorporated herein by reference. The CPB system has an arterial return cannula which is used to return oxygenated blood to the patient. An aortic occlusion catheter passes through the arterial cannula. The aortic occlusion catheter is used to block blood flow through the ascending aorta and deliver cardioplegic fluid to arrest the heart for performing surgery on the heart and great vessels. The aortic occlusion catheter is inserted through the same lumen in the arterial cannula which is used to return arterial blood to the patient so that the arterial blood essentially passes in the annular space between the aortic occlusion catheter and the arterial return cannula.
An advantage of the CPB system described above is that only one opening in the patient's arterial system is required for both delivery of cardioplegic fluid and return of arterial blood. In order to achieve optimum blood and cardioplegic fluid flow rates, the wall of the arterial cannula must be minimized while retaining enough structural integrity to prevent kinking and/or cracking. The present invention is particularly useful in providing a thin walled cannula which may be used as an arterial return cannula for the system described above.
A known method of making a reinforced cannula is to dip a mandrel in a polymer solution and wrap a metal wire over the polymer. The mandrel is then dipped again to encase the metal wire between two layers of polymer.
Another known method of making a reinforced cannula is to extrude a polymer tubing, wrap a metal wire around the polymer tubing, and extrude another polymer layer over the metal wire.
A problem with the known methods of manufacturing a reinforced cannula is that the spacing between adjacent wires must be relatively large to ensure that the polymer flows between adjacent coils so that the two polymer layers bond together to form an integrated structure. Unfortunately, the relatively large spacing requires a relatively thick polymer layer to provide the necessary strength since the wire has a large pitch. The relatively thick polymer layer is also required to ensure that a sufficient amount of polymer is provided to fill the relatively large space. The resulting cannula has a relatively thick wall.
Thus, a specific object of the present invention is to provide a new method of manufacturing reinforced tubing and, in particular, cannulas for venous withdrawal and arterial return of blood for a cardiopulmonary bypass system.